In recent years, some techniques have been developed to detect an object such as a vehicle by measuring radio waves radiated from the object. As an example thereof, Japanese Patent Application Publication No. 2006-322833 is disclosed. The radio wave receiving system disclosed in Japanese Patent Application Publication No. 2006-322833 detects a vehicle by detecting the profile of the windshield or hood of the vehicle from the received radio waves.
However, the above radio wave receiving system disclosed in Japanese Patent Application Publication No. 2006-322833 is configured to recognize a vehicle by detecting the profile of a part of the vehicle, and therefore has a problem that false detection may be caused due to the presence of another object having a similar profile.